Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.85   4.125%   $70.6488   $70.65   $70.65   $70.60  
  Purchase #2 $163.41   3.151%   $168.559   $168.56   $168.55   $168.60  
  Purchase #3 $152.99   11.179%   $170.0928   $170.09   $170.10   $170.10  
  Purchase #4 $181.92   7.347%   $195.2857   $195.29   $195.30   $195.30  
  Purchase #5 $233.43   5.608%   $246.5208   $246.52   $246.50   $246.50  
  Purchase #6 $116.37   6.793%   $124.275   $124.28   $124.30   $124.30  
  Purchase #7 $58.82   5.729%   $62.1898   $62.19   $62.20   $62.20  
  7 purchase totals = $974.79       $1,037.5719   $1,037.58   $1,037.60   $1,037.60